The present invention relates to CNC operation, and more particularly to a progrdmmed path control method of tool withdrawal and resumption in CNC operation.
A continuous and uninterrupted CNC operation is an objective to be accomplished by the manufacturers of factory automation; nevertheless it is often difficult to keep CNC operation in progress steadily during a lengthy machining process. The manufacturers of CNC machineries are therefore interested in developing the technology capable of diagnosing the operational condition of the CNC machinery to prevent the machinery from being damaged accidentally by an unforeseen situation brought about sporadically and to avoid an unnecessary delay in the production process.
When the machining process is found to be in trouble, the CNC operation in progress must be first stopped to allow the machine operator to withdraw the tool manually from its working position so as to correct the situation in order to permit the interrupted tool to resume its operation from the process point at which it was interrupted previously. If the discharge process of CNC is found to be operating abnormally, it is then very likely that the withdrawal of the electrode is called for. Under such circumstance, an automatically controlled method of tool withdrawal and resumption is needed in order to improve the production efficiency.
It is a well-known fact that the operational control of a CNC machinery is generally achieved by means of interpolation, which undertakes the linear or circular arc blocks based on the operational information transmitted from a specific part program of the CNC machinery, and that it is a rather tedious and time-consuming task to withdraw the tool until such time when the interrupting culprits are corrected and subsequently to make the withdrawn tool to move back to the point, where it was interrupted previously, in order to be ready to resume its unfinished job. According to the technology used currently in the CNC electroerosion process, the path of tool withdrawal is specifically controlled by a vector method, in which the electrode is made to withdraw immediately in that direction as soon as the discharge process of CNC is operating erratically, and in which the electrode is made to return to the point, where it was interrupted, along the original path of its withdrawal when the discharge process of CNC is made to resume its operation regularly. However, such method as described above is limited in that it is not provided with means to drive the cutting tool or electrode to a certain end position in order to let CNC check on the abnormal process.